Process for the activation of zeolitic catalysts containing titanium and their use in oxidation reactions

ABSTRACT

A process is described for the activation of zeolitic catalysts containing titanium having the formula: xTiO 2 (1-x)SiO 2  wherein x ranges from 0.0001 to 0.4, which consists in treating said materials with a solution of an ammonium salt of a carboxylic acid and subsequently subjecting them to calcination. The catalysts thus treated have higher catalytic performances with respect to those not treated, in oxidation processes of organic substrates.

This application is a 371 of PCT/EP02/06500 filed Jun. 12, 2002.

The present invention relates to a process for the activation ofzeolitic catalysts containing titanium having formula (I):xTiO₂(1−x)SiO₂  (I)wherein x ranges from 0.0001 to 0.4.

More specifically, the invention relates to a process for the activationof zeolitic catalysts which consists in treating said materials with asolution of an ammonium salt of a carboxylic acid and subsequentlysubjecting them to calcination.

The invention also relates to the materials obtained by means of theabove process and to processes in which they are used as catalysts.

Zeolites, and zeolitic materials in general, are basic components forthe preparation of catalysts used in numerous reactions of industrialinterest.

For example, zeolites of the MFI type are known in literature as basematerial for the preparation of catalysts which can be used in there-arrangement reaction of oximes to amides (EP 242,960).

Zeolites of the MFI type, in which the heteroelement supporting siliconis titanium (Titanium Silicalites TS-1), are known as catalysts used inmany oxidation reactions (U.S. Pat. Nos. 4,410,501; 4,794,198).

It is also known in literature that the performances of zeoliticcatalysts used in oxidation reactions in which the oxidant adopted ishydrogen peroxide added or produced by compounds capable of generatingit under the reaction conditions, can be effectively improved bysubjecting these catalysts to suitable activation treatment.

For example, in patent EP 230,949, the titanium silicalite pretreatedwith a suitable neutralizing agent of acid groups improves itsselectivity in the epoxidation reactions of olefinic compounds withhydrogen peroxide.

It is known, however, that these agents, in particular those of alkalineand/or earth alkaline metals, reduce the catalytic activity more or lesssignificantly, referring to the conversion rate of H₂O₂ in the timeunit. In addition, they accumulate in the catalyst itself, making thethermal regeneration of the catalytic activity problematical, both interms of maintaining the structural stability of the catalyst and alsothe refractory resistance in the calcination ovens where theregeneration is effected.

In patent EP 267,362, the titanium silicalite TS-1 pretreated withaqueous solutions of hydrogen peroxide and/or in the presence of atleast 0.5 equivalents/liter of acids with a pK_(a)≦5 (preferably H₂SO₄,HCl, HNO₃, H₃PO₄), is particularly active in ammoximation reactions ofcarbonyl compounds.

In patent EP 958,861, the titanium silicalite TS-1 after activationtreatment with fluoride ions or species containing fluoride, in anaqueous medium in the presence of hydrogen peroxide, improves thecatalytic properties in ammoximation processes.

The activation treatment described above, however, has the greatdisadvantage of using chemical agents which are not easy to handle interms of transportation, storage and use, as they create seriousproblems relating to corrosion of the materials and, above all, thedisposal and treatment of the resulting process waste products.

It is also known that the action of these agents, with particularreference to hydro-halogen acid, results in the destructuration, bycomplexing, of the titanium creating a final TiO₂ phase which iscatalytically inactive (EP 958,861).

A process has now been surprisingly found which, in addition toeffectively activating zeolitic materials containing titanium inoxidation reactions with hydrogen peroxide, or compounds capable ofgenerating it under the reaction conditions, also overcomes thedrawbacks described above.

In particular, an object of the present invention relates to a processfor improving the catalytic performances in oxidation reactions withzeolitic catalysts containing titanium having formula (I):xTiO₂(1−x)SiO₂wherein x ranges from 0.0001 to 0.4, preferably from 0.001 to 0.04 andmore preferably from 0.01 to 0.03, which consists in subjecting thecatalyst to treatment with an aqueous and/or aqueous-organic solution ofan ammonium salt of a mono-, bi-, tri-, tetra-carboxylic acid, linear orbranched, with a total number of carbon atoms ranging from 2 to 20,having general formula (II):

wherein one of the R groups is a carboxyl whereas the other R groups,the same or different, can be selected from hydrogen, hydroxyl, ether,ester, carbonyl, carboxyl, amine, amide, vinyl, hydro-halogen, nitrile,hydro-sulfide, sulfonic, phosphonic groups, etc.; or they can beselected from alkyl, cycloalkyl, alkylcycloalkyl, aromatic,alkylaromatic, aralkyl and hetero-aromatic groups, in turn substitutedwith one or more atoms or groups selected from hydrogen, hydroxyls,carboxyls, halogens, alkoxides, amines, esters, amides, vinyls,nitrites, hydroxyls, hydrosulfides, carbonyls, etc.; the central carbonatom of general formula (II) may or may not belong to a cycle, which canbe saturated or unsaturated, hetero-aromatic with one or morehetero-atoms selected from N, O, S, etc. or non-hetero-aromatic; in thecase of a cyclic substituent in formula (II), two adjacent R groups areimmediately bound to the central carbon and contemporaneously belong tothe cycle; this treatment is carried out for a time ranging from 0.2 to5 hours, at concentrations of ammonium salt ranging from 0.2 to 10% byweight and is followed by the separation of the catalyst by filtrationand its calcination at temperatures ranging from 300 to 650° C. for aperiod of time ranging from 1 to 6 hours.

In particular, examples of ammonium carboxylates useful for the purposesof the present invention are those of carboxylic acids having a pK_(a)within the range of 4.00 to 5.15, preferably from 4.55 to 4.95, andwhich in solution develop a pH ranging from 6.6 to 7.4 and, morespecifically from 6.9 to 7.1.

Acetic, tartaric, citric, hydroxybutyric, aminobenzoic,hexahydrobenzoic, phthalic and pyridinecarboxylic acids have proved tobe particularly suitable for the purposes of the invention.

Titanium silicalites in which part of the titanium is substituted byother metals such as boron, aluminum, iron or gallium, can also besubjected to treatment. These substituted titanium silicalites and theirpreparation methods are described in published European patentapplications 226,257, 226,258, 266,825 and 293,032.

The treatment of the catalyst according to the invention causes anexpansion in the volume of the unitary cell with respect to the initialvalue, as can be observed from Rietveld refinement of the XRDdiffraction spectrum. Furthermore, XPS spectroscopy of the TS-1 sampletreated, for example with ammonium acetate, shows that the width atmid-height of the carbon signal C(1s), centred at a Binding Energy, BE,of 285.0 eV, increases from 3.0 to 3.7 eV with respect to thenon-treated sample. In particular, the C(1s) peak of the treated samplehas a shoulder at a BE of 287.0 eV, which can be correlated to an estergroup, not present in TS-1 as such, and which can also be observed afterthermal treatment. The Si(2p) and Ti(2p) signals also broaden from 2.8to 3.4 eV and from 3.3 to 3.9 eV, respectively, indicating a greaterheterogeneity of species present after treatment with ammonium acetate.

The increase in the cell volume, on the other hand, is not observed whenthe treatment is effected with salts of carboxylic acid in which theammonium ion is substituted, for example, with alkaline and/or earthalkaline cations (EP 230,949). When the treatment is effected with asodium carboxylate, a contraction effect of the cell volume actuallytakes place (Example 2 and Table 1).

When, on the other hand, it is the carboxylate anion of the ammoniumsalt which is substituted with acid anions different from thosespecified above, as in the case, for example, of salts of ammoniumchloride, ammonium bicarbonate, ammonium hydrate, a lesser expansion isobtained after calcination, equal to about half, of the cell volume ofthe catalyst (Examples 3, 4 and Table 1).

The presence of the ammonium ion, with a pK_(a) of 9.25, in the salts ofthe invention makes it possible to have the necessary molarities fortreating the catalyst without modifying the pH of the treatment solutionwhich, in the case of the invention ranges from 6.6 to 7.4, preferablyfrom 6.9 to 7.1.

The ammonium salts used in the treatment also have the particularcharacteristic of being able to be easily and completely removed in thesubsequent thermal treatment of the catalyst, before its use, as theammonium ion is completely degraded and removed from the zeoliticstructure as well as the anions selected from the acids mentioned above.This ensures the elimination of any undesirable intervention phenomenonof the cation on the structure (modification of the crystalline class,introduction of defects, partial or complete mineralization of thestructure itself) observed with other cations indicated in the known art(EP 230,949). It should be pointed out that in the known art, the use ofammonium carboxylates or other ammonium salts is exclusively connectedto the use of these agents for washing zeolitic catalysts beforespectroscopic analyses to remove organic residues (for exampletemplating agents) and/or inorganic residues (for example Al and Fe)released from the materials of the synthesis plant or present asimpurities in the precursors. The known art, however, does not provideany indication as to the operating procedure of the treatment orproperties and/or catalytic applications of the zeolitic catalysts thustreated (R. Millini et al., J. Catalysis, 137, 497–503, 1992; C.Lamberti et al., J. Catalysis, 183, 222–231, 1999).

From a procedural point of view, the treatment according to the presentinvention can be effected by reflux boiling, incipient wetnessimpregnation or fixed bed percolation. These treatment techniques arepreferred as they are easy to effect and at the same time extremelyeffective.

The ref lux boiling treatment is carried out by the adequate stirring ofa suspension of the catalyst in an aqueous or aqueous-organic solutionof the salt, and by raising the temperature to the reflux value of thesuspension.

In the activation phase of the catalyst, the concentration of saltpresent in the treatment solution ranges from 0.2 to 10% by weight ofthe solution itself, preferably from 2 to 6%, more preferably from 3 to5%.

The treatment is carried out for a time ranging from 0.5 to 5 hours,preferably from 0.5 to 3 hours and more preferably from 0.75 to 1.5hours.

The solutions selected for the treatment can be aqueous oraqueous-organic; the organic solvent can be polar and therefore selectedfrom alcohols, ketones, nitrites, amides, etc., or apolar such asesters, ethers, paraffins, aromatics, etc.

The catalyst is separated from the solution by filtration and, withoutbeing subjected to any washing operation, is placed directly in muffleto be calcined at temperatures ranging from 300 to 650° C. andpreferably from 450 to 600° C. for a time range varying from 1 to 6hours, preferably from 3 to 5 hours.

The calcination temperature is reached at rates ranging from 1 to 30°C./min, preferably from 5 to 20° C./min.

With the incipient wetness technique, a preliminary drying is effectedat 105–110° C., under vacuum, of the titanium silicalite, followed bythe actual impregnation with a solution having a volume equal to thepore volume of the catalyst and with an adequate salt content, afterwhich it is filtered, and calcined at 550° C. for 3–5 hours.

With the fixed bed percolation technique, the solution and/or suspensionof the salt is percolated on the catalyst to be treated, contained in atubular jacketed reactor. The eluate is recovered in a tank andre-circulated with a pump to the reactor for a number of times which issufficient to exchange the desired concentration on the catalyst.

Alternatively, it is possible to percolate the solvent alone, whichelutes a fine layer of the salt, arranged on the upper part of thecatalyst. The percolated product may, also in this case, be convenientlyrecycled, after the first passage, onto the catalyst.

The catalyst is charged and homogeneously packed into the reactor so asto eliminate preferential infiltrations of the liquid through the solid,ensuring treatment homogeneity.

The process of the present invention, although being generally valid forthe activation of TS-1 in the oxidation reactions of organic substrateswith hydrogen peroxide, or compounds capable of producing it under thereaction conditions, has proved to be particularly useful inammoximation reactions of carbonyl compounds, such as, for example,cyclohexanone (U.S. Pat. No. 4,794,198; EP 496,385).

EXAMPLE 1

10 g of TS-1 EniChem catalyst, containing 2.93% w/w of total TiO₂determined by XRF (X-ray fluorescence), and 20 g of NH₄OOCCH₃ (NH₄Ac)(Carlo Erba RPE-ACS, min. tit. 98%) in 500 mL of H₂O, corresponding to amolar ratio R_(M)(Ac/Ti)=1.5, are charged into a 1000 mL flask equippedwith a mechanical stirrer, reflux condenser, thermometer andthermostat-regulated jacket. The aqueous suspension of the catalyst isheated to reflux temperature and maintained at this value for 1 hour.

After treatment with NH₄Ac, the catalyst is separated from the solutionby filtration, not washed with H₂O (or other solvents), placed inmuffle, heated at 5° C./min to 550° C. and kept at this temperature for5 hours. XRF analysis on the catalyst thus obtained indicates a totalcontent of TiO₂ equivalent to the initial value. XRD diffractometricanalysis also shows an orthorhombic structure and, by means of Rietveldrefinement of the spectrum, an increase in the cell volume is calculatedof about 14–17 Å³, from the initial value of 5371 Å³ to the final valueof 5385–5388 Å³.

EXAMPLE 2

10 g of the same catalyst as Example 1 are treated with 500 mL of anaqueous solution in which 20 g of diammonium citrate (NH₄Cit) have beenpreviously dissolved. After the treatment, the catalyst is separated byfiltration, and placed directly in muffle, without intermediate washing,at 550° C. for 5 hours. XRF analysis on the catalyst thus obtainedindicates a total content of TiO₂ equivalent to the initial value of2.93%. XRD diffractometric analysis also shows an orthorhombic structureand, by means of Rietveld refinement of the spectrum, an increase in thecell volume is calculated of about 17 Å³, from the initial value of 5371Å³ to the final value of 5388 Å³.

EXAMPLE 3 Comparative

10 g of the same catalyst as Example 1 are treated with 500 mL of anaqueous solution in which 20 g of sodium acetate (NaOOCCH₃, NaAc) havebeen previously dissolved. After the treatment, the catalyst isseparated by filtration, and placed directly in muffle at 550° C. for 5hours. XRF analysis on the catalyst thus obtained indicates a totalcontent of TiO₂ equivalent to the initial value of 2.93%. XRDdiffractometric analysis also shows an orthorhombic structure and, bymeans of Rietveld refinement of the spectrum, a decrease in the cellvolume is calculated of about 10 Å³, from the initial value of 5371 Å³to the final value of 5361 Å³.

EXAMPLE 4 Comparative

Three samples, of 10 g each, of the same catalyst as Example 1 arerespectively treated with an aqueous solution 0.44 M of ammoniumchloride (NH₄Cl), 0.50 M of ammonium bicarbonate (NH₄HCO₃) and 7.7 M ofammonium hydrate (NH₄OH). After each treatment, each catalyst isseparated by filtration, and placed directly in muffle at 550° C. for 5hours. Table 1 indicates the results of XRD diffractometric analysiswhich show that the orthorhombic structure has been maintained and, bymeans of Rietveld refinement, the unitary cell parameters. With respectto the expansion of the cell volume, 14–18 Å³, determined for ammoniumacetate and citrate, in all three cases, regardless of the pH value ofthe treatment solutions, a more limited expansion is observed, of about8 Å³, compared to the initial value of TS-1 as such of 5371 Å³.

TABLE 1 Structural parameters for TS-1 not treated and treated withsolutions of NH₄Ac, NH₄Cit, NH₄Cl, NH₄HCO₃, NH₄OH and NaAc havingvarying molarities. Calcination at 550° C. Solution molarity a b c β VSalt (moles/L) (Å) (Å) (Å) (Å) (Å³) R_(p) R_(wp) — — 20.10125(83)19.92990(83) 13.40730(64) 90 5371.1(0.5) 4.42 5.6  NH₄Ac 0.5220.12705(91) 19.94886(76) 13.42027(85) 90 5388.4(0.6) 3.38 4.39 NH₄Ac2.86 20.12458(93) 19.94509(90) 13.41879(62) 90 5386.1(0.6) 3.54 4.44NH₄Ac 4.42 20.12443(74) 19.94229(77) 13.41918(63) 90 5385.5(0.4) 4.525.69 NH₄Cit 0.18 20.12959(61) 19.94728(67) 13.42011(52) 90 5388.6(0.3)3.86 4.93 NH₄Cit 1.00 20.13083(69) 19.95053(75) 13.41573(68) 905388.0(0.6) 3.41 4.34 NH₄Cit 2.00 20.12553(86) 19.94706(71) 13.42027(56)90 5387.5(0.3) 4.65 5.99 NH₄Cl 0.44 20.10792(63) 19.93869(71)13.41153(57) 90 5377.0(0.3) 4.08 5.34 NH₄HCO₃ 0.50 20.10871(88)19.93764(91) 13.41304(72) 90 5377.5(0.4) 5.46 7.42 NH₄OH 7.7020.11265(75) 19.93913(78) 13.41483(60) 90 5379.7(0.4) 4.21 5.48 NaAc0.49 20.09981(98) 19.90882(79) 13.39760(88) 90 5361.2(0.5) 3.75 4.87X ray diffraction—WAXS: Cu K_(α) Ni filtered, E 40 KV—140 mA, range14–101 °2Θ, step 0.02 °2Θ, t6.5 per step. R_(p) and R_(wp) reliabilityfactors of Rietveld refinement.

EXAMPLE 5

An ammoximation reaction of cyclohexanone in a continuous manner isdescribed, using the catalyst prepared according to the procedure ofExample 1.

The reaction is carried out in equipment consisting of a 1 L steelautoclave equipped with a mechanical stirrer, automatic level control,thermostat-regulation, a device for operating at constant pressure,separate inlets for the reaction solvent, cyclohexanone and for thesolution of hydrogen peroxide, and an outlet for the reaction solutionequipped with a filter plug having a suitable porosity for keeping thecatalyst inside the reactor.

The reaction is activated by feeding, at a constant volume in thereactor equal to 0.5 L, the reaction solvent, consisting of anazeotropic mixture of t-butyl alcohol and water (88/12 w/w) in which thenecessary concentration of gaseous NH₃ has been previously absorbed (atleast 2.5% with respect to the liquid phase), and 8.1 g of the catalystof Example 1 (equal to 1.9% of the solution in the reactor) maintainedunder suspension by adequate stirring.

Once the reactor has been brought to a temperature of 85° C. and apressure of 2.5 ata, maintained during the whole duration of the testwith He, the solution of hydrogen peroxide and cyclohexanone is fed.

254.4 g/h (59% w of the solution in the reactor) of t-butyl alcohol,34.7 g/h (8% w) of water, 23.9 g/h (5.5% w) of NH₃, 50.9 g/h of anaqueous solution of H₂O₂ with a titer of 50.01% w (equal to 5.9% w ofH₂O₂ 100%) and 67.2 g/h (15.6% w) of cyclohexanone (One), are fed, underregime conditions, in the test described herein.

In this way, the following molar ratios (R_(M)) are obtained, insolution:R_(M)(H₂O₂/One)=1.09; R_(M)(NH₃/One)=2.04; R_(M)(NH₃/H₂O₂)=1.87.

The test was carried out, under these conditions, without effecting anycatalyst make-up, until exhaustion of the catalytic activity, obtainingthe following results:

Test duration time: 310 hours Conversion of One: 98.6% mol (during test)Selectivity to Oxime: 99.9% mol Yield of One to Oxime: 98.5% mol Yieldof H₂O₂ to Oxime: 90.4% mol Specific catalyst consumption: 0.35g_(cat)/Kg_(oximeproduced)

EXAMPLE 6 Comparative

Using the same equipment and operating procedure described in Example 3,an ammoximation reaction of cyclohexanone was carried out in acontinuous manner using however 8.1 g (1.9% w of the solution in thereactor) of TS-1 EniChem catalyst without any subsequent treatment (assuch).

In this way, the following molar ratios (R_(M)) were registered, underregime conditions, in the reaction solution of this test:R_(M)(H₂O₂/One)=1.10; R_(M)(NH₃/One)=2.02; R_(M)(NH₃/H₂O₂)=1.84.

The test was carried out, under these conditions, without effecting anycatalyst make-up, until exhaustion of the catalytic activity, obtainingthe following results:

Test duration time: 137 hours Conversion of One: 97.9% mol (during test)Selectivity to Oxime: 99.6% mol Yield of One to Oxime: 97.5% mol Yieldof H₂O₂ to Oxime: 90.1% mol Specific catalyst consumption: 0.79g_(cat)/Kg_(oximeproduced)Table 2 below gives a direct comparison between Examples 5 and 6. It canbe observed that the performances of the catalyst treated with NH₄Ac,Example 5, are much higher than those of the non-treated catalyst (assuch), Example 6.

TABLE 2 Example 6 Example 5 Catalyst Catalyst Performances Unit TS-1 assuch TS-1 NH₄OCOCH₃ One conversion mol. % 97.9 98.6 Selectivity to oxime″ 99.6 99.9 One yield to oxime ″ 97.5 98.5 H₂O₂ yield to oxime ″ 90.190.4 Test duration hr 137 310 Catalyst specific g_(cat)/kg_(oxime) 0.790.35 consumption

1. A process comprising ammoximation of a carbonyl compound in thepresence of hydrogen peroxide or a compound capable of producinghydrogen peroxide, and a zeolitic catalyst containing titanium havingformula (I) xTiO₂(1−x)SiO₂ (I), wherein x ranges from 0.000 1 to 0.4,said catalyst being obtained by a process which comprises subjecting thecatalyst to treatment with an aqueous and/or aqueous-organic solution ofan ammonium salt of a mono-, bi-, tri-, tetra-carboxylic acid, linear orbranched, with a total number of carbon atoms ranging from 2 to 20,having general formula (II)

wherein one of R1, R2, R3 and R4 is a carboxyl group, and the others ofR1, R2, R3 and R4, the same or different, are selected from the groupconsisting of hydrogen, hydroxyl, ether, ester, carbonyl, carboxyl,amine, amide, vinyl, hydro-halogen, nitrile, hydro-sulfide, sulfonic,and phosphoric groups; or are selected from the group consisting ofalkyl, cycloalkyl, alkylcycloalkyl, aromatic, alkylaromatic, aralkyl andhetero-aromatic groups, which groups are unsubstituted or substitutedwith one or more atoms or groups selected from the group consisting ofhydrogen, hydroxyl, carboxyl, halogen, alkoxide, amine, ester, amide,vinyl, nitrile, hydroxyl, hydro-sulfide and carbonyl; wherein thecentral carbon atom of general formula (II) may optionally form a cyclewith two adjacent groups from R1, R2, R3 and R4, which cycle issaturated or unsaturated, hetero-aromatic with one or more hetero-atomsselected from the group consisting of N, O, S, or non-hetero-aromatic;which treatment is carried out for a time ranging from 0.2 to 5 hours,at concentrations of ammonium salt ranging from 0.2 to 10% by weight andis followed by the separation of the catalyst by filtration and itscalcination at temperatures ranging from 300 to 650° C. for a period oftime ranging from 1 to 6 hours.
 2. The process according to claim 1,wherein the catalyst is titanium silicalite TS-1 and x ranges from 0.001to 0.04.
 3. The process according to claim 2, wherein x ranges from 0.01to 0.03.
 4. The process according to claim 2, wherein in the silicaliteTS-1 part of the titanium is substituted by a metal.
 5. The processaccording to claim 4, wherein the metal comprises boron, aluminum, ironor gallium.
 6. The process according to claim 1, wherein the ammoniumsalt is of a carboxylic acid having a pK_(a) ranging from 4.00 to 5.15.7. The process according to claim 6, wherein the carboxylic acid has apK_(a) ranging from 4.55 to 4.95.
 8. The process according to claim 7,wherein the carboxylic acid is selected from the group consisting ofacetic, tartaric, citric, hydroxybutyric, aminobenzoic,hexahydrobenzoic, phthalic and pyridinecarboxylic acid.
 9. The processaccording to claim 1, wherein the pH of the aqueous and/oraqueous-organic solution ranges from 6.6 to 7.4.
 10. The processaccording to claim 9, wherein the pH ranges from 6.9 to 7.1.
 11. Theprocess according to claim 1, wherein the concentration of salt rangesfrom 2 to 6%.
 12. The process according to claim 10, wherein theconcentration of salt ranges from 3 to 5%.
 13. The process according toclaim 1, wherein the treatment is carried out for a time ranging from0.5 to 3 hours.
 14. The process according to claim 13, wherein thetreatment is carried out for a time ranging from 0.75 to 1.5 hours. 15.The process according to claim 1, wherein treatment is carried out withsaid aqueous-organic solution and the solvent of the aqueous-organicsolution is a polar solvent selected from the group consisting ofalcohols, ketones, nitriles, and amides, or an apolar solvent selectedfrom the group consisting of esters, ethers, paraffins, and aromatics.16. The process according to claim 1, wherein the catalyst is calcinedat temperatures ranging from 450 to 600° C. and for a time range varyingfrom 3 to 5 hours.
 17. The process according to claim 1, wherein thecalcination temperature is reached at rates ranging from 1 to 30°C./min.
 18. The process according to claim 17, wherein the calcinationtemperature is reached at rates ranging from 5 to 20° C./min.
 19. Theprocess according to claim 1, wherein the carbonyl compound iscyclohexanone.